Process for the preparation of glycol ethers

ABSTRACT

A process for the preparation of a glycol ether by reacting an olefin oxide with an excess of an alcohol over a catalyst; characterized in that the catalyst comprises a material which has been prepared by calcination of an anionic double hydroxide clay having a structure comprising magnesium and aluminum in combination, followed by rehydration and subsequent recalcination.

This invention relates to a process for the preparation of glycolethers.

Glycol ethers are useful as jet anti-icing fluids, brake fluid blendingcomponents and solvents for paints, inks and the like. They may beproduced by reacting an alcohol with an olefin oxide in the presence ofeither a basic or acidic catalyst.

Anionic double hydroxide clays are well-known materials. They aredescribed in, for example, "Anionic Clay Minerals", W. T. Reichle,"Chemtec", January 1986. They consists of positively charged metaloxide/hydroxide sheets with intercalated anions and water molecules. Interms of charge they are mirror-images of the much studied family ofcationic clay minerals. The structure of anionic double hydroxide claysis related to that of brucite, Mg(OH)₂. In brucite magnesium isoctahedrally surrounded by six oxygens in the form of hydroxide; theoctahedral units then, through edge sharing, form infinite sheets. Thesheets are stacked on top of each other by hydrogen bonds. If some ofthe magnesium in the lattice is isomorphously replaced by a highercharged cation, e.g. Al³⁺, then the resulting overall single Mg²⁺ --Al³⁺--OH layer gains a positive charge. Sorption of an equivalent amount ofhydrated anions renders the structure electrically neutral, resulting inan anionic double hydroxide clay.

Anionic double hydroxide clays have, in the dehydrated form, theempirical formula:

    [M.sub.a.sup.2+ N.sub.b.sup.3+ (OH).sub.(2a+2b) ][X].sub.b

in which M²⁺ is a divalent metal cation; N³⁺ is a trivalent metalcation; X is one equivalent of an anion; and a and b represent therelative proportions of M and N in the structure. Typically, M²⁺ isMg²⁺, Fe²⁺, Co²⁺, Ni²⁺ and/or Zn²⁺, and N³⁺ is Al³⁺, Cr³⁺ and/or Fe³⁺.In an alternative form, the divalent metal may be wholly or partlyreplaced by lithium, the all-lithium form having the empirical formula:

    [Li.sub.a.sup.+ N.sub.b.sup.3+ (OH).sub.(a+b) ][X].sub.2b

In the naturally-occurring minerals hydrotalcite and mannaseite, M²⁺ isMg²⁺, N³⁺ is Al³⁺, X is carbonate, and a/b is in the range of 1:1 to5:1. Such minerals occur in a hydrated form.

U.S. Pat. No. 4,458,026 discloses that catalysts prepared by calcinationof anionic double hydroxide clays may be used to perform aldolcondensations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the percent of conversion of propylene oxideversus the time on stream for glycol ether preparation using the methodof the present invention and using a method which does not use arehydrated and calcined catalyst.

FIG. 2 is a graph showing the percent of conversion of propylene oxideversus the time on stream for glycol ether preparation using the methodof the present invention and using a method which is a variation of thepresent invention.

The present invention provides a process for the preparation of a glycolether by reacting an olefin oxide with an excess of an alcohol over acatalyst; characterised in that the catalyst comprises a material whichhas been prepared by calcination of an anionic double hydroxide clay.

Preferably the anionic double hydroxide clay has a framework structurecomprising magnesium and aluminium.

Anionic double hydroxide clays can be prepared by known methods, forexample by the method described in U.S. Pat. No. 4,458,026. In general,solutions of soluble salts of the relevant metals are mixed togetherwith an alkali metal hydroxide and an alkali metal carbonate. Theresulting mixture is vigorously stirred until a slurry is formed. Theslurry is then heated, typically to a temperature between 50° and 100°C., preferably 60° to 75° C., until sufficient crystallisation occurs.

In order to prepare the catalyst required for the process of theinvention, the anionic double hydroxide clay is subjected tocalcination. Preferably this involves heating to a temperature of atleast 300° C., preferably 300° to 550° C., especially 400° to 500° C.,under non-reducing conditions. The heating may be carried out undervacuum, in an inert gas or, preferably, in an oxidising atmosphere,preferably air. Heating is carried out for a period of time typicallybetween 10 and 30 hours. Such treatment causes the collapse of thedouble hydroxide layered structure, and, generally, results in an oxidematerial having a structure related to that of MgO.

The calcined anionic double hydroxide clay may be used directly as thecatalyst for the preparation of glycol ethers. However, we have foundthat the catalytic activity of the material is enhanced if the calcinedmaterial is rehydrated and subsequently recalcined. Such procedure isparticularly effective when the rehydration is carried out using watersubstantially free from dissolved ions, particularly decarbonated water.Suitable decarbonated water may be prepared by purging distilled ordeionised water with an inert gas, for example nitrogen, argon orhydrogen, to remove carbon dioxide and hence carbonate ions. Rehydrationmay be carried out simply by soaking for an adequate period of time,typically from 10 to 30 hours, and then recalcining the material by thesame method as used for the initial calcination. Suchrehydration/recalcination treatment may if desired be carried out anumber of times, with beneficial results, especially when using amaterial containing magnesium and aluminium.

The alcohol used in the process according to the invention may be analiphatic, cycloaliphatic or aromatic alcohol, preferably having up to 8carbon atoms. An aliphatic alcohol preferably has up to 6, morepreferably up to 4, carbon atoms. Typical aliphatic alcohols includemethanol and ethanol. An example of a suitable cycloaliphatic alcohol iscyclohexanol, and an example of a suitable aromatic alcohol is phenol.More than one alcohol group may be present if desired, but preferablythe alcohol is a mono alcohol. Mixtures of alcohols may be used ifdesired. The alcohol must be used in excess to produce the desiredglycol ether and suppress the formation of oligomeric products.Preferably the molar ratio of alcohol to olefin oxide is at least 2:1,especially at least 5:1, most preferably at least 10:1.

The olefin oxide preferably has up to 10, especially up to 8, carbonatoms, and may for example be derived from an alkene, for example etheneor propene, or from an arylalkene such as styrene.

In a preferred embodiment of the invention, ethanol is reacted withpropylene oxide to produce a mixture of the primary and secondary glycolethers, 2-ethoxy-1-propanol and 1-ethoxy-2-propanol. It is a majoradvantage of the process according to the present invention that thereaction proceeds with a very high selectivity to the secondary product,which is in general the desired product.

The reaction may be carried out in the vapour phase or, especially, theliquid phase. The optimum reaction temperature will of course dependupon the particular reactants used, but will in general be within therange of from 0° to 200° C., especially 70° to 150° C. The reaction maybe carried out at atmospheric or elevated pressure, for example up to100 barg.

The following Examples illustrate the invention. Examples 1 to 8illustrate the synthesis of anionic double hydroxide clays; Examples 9and 22 to 28 illustrate calcination of anionic double hydroxide clays toproduce active catalysts; and Examples 10 to 21 and 29 to 33 illustratethe use of these catalysts in the production of glycol ethers. Example34 is a comparative example.

EXAMPLE 1 Preparation of a Magnesium/Aluminium/Carbonate Anionic DoubleHydroxide Clay

A solution of 256 g Mg(NO₃)₂.6H₂ O(1.00 mole) and 187.5 g Al(NO₃)₃.9H₂ O(0.50 moles) in 700 ml deionised water was added dropwise to a solutionof 140 g NaOH (3.5 mole) and 100 g anhydrous Na₂ CO₃ (0.943 mole) in1000 ml deionised water. The addition was carried out in a 3 liter flaskand uniform mixing was achieved by use of a mechanical stirrer. Using acooling bath, the temperature was maintained at about 35° C. duringsolution which took about 4 hours. A heavy slurry was formed. The flaskcontents were then transferred to a thermal bath and heated to andmaintained at 65±2° C. for 18 hours with continuous stirring. Thereafterthe resulting thick slurry was filtered and washed with a large excessof deionised water. The solid was then dried at 125° C. either in vacuumor air for 18 hours. The resulting white powder gave an X-ray powderdiffraction profile of hydrotalcite. This profile is shown in TableXRD-1.

Elemental analysis: 11.99% Al; 19.08% Mg; 2.60% C. This corresponds toan empirical formula of Mg₆ Al₃.3 (OH)₁₈.6 (CO₃)₁.7 4H₂ O.

²⁷ Al magic angle spinning nmr gave a single peak of chemical shift 8.3ppm, corresponding to all the aluminium being in octahedralcoordination.

EXAMPLE 2 Preparation of a Magnesium/Iron/Carbonate Anionic DoubleHydroxide Clay

Example 1 was repeated except that a solution of 25.6 g Mg(NO₃)₂. 6H₂ O(0.10 moles) and 13.45 g Fe(NO₃)₃. 9H₂ O (0.033 moles) in 70 ml waterwas added dropwise to a 100 ml solution of NaOH (12 g, 0.30 moles) andNa₂ CO₃ (10 g, 0.094 moles). The XRD of the product is shown in TableXRD-2.

Elemental analysis: 2.09% C; 21.3% Mg; 17.9% Fe. This corresponds to anempirical formula of Mg₆ Fe₂.2 (OH)₁₆.4 (CO₃)₁.1. 4H₂ O.

EXAMPLE 3 Preparation of a Nickel/Aluminium/Carbonate Anionic DoubleHydroxide Clay

Example 1 was repeated except that a solution of Ni(NO₃)₃. 6H₂ O (29.1g, 0.10 moles) and Al(NO₃)₃. 9H₂ O (12.5 g, 0.033 moles) in 70 mldeionised water was added slowly to an aqueous solution of NaOH (12.0 g,0.30 moles) and Na₂ CO₃ (10 g, 0.094 moles) in 100 ml deionised water.The XRD of the product is shown in Table XRD-3.

Elemental analysis: 1.75% C.

EXAMPLE 4 Preparation of a Zinc/Chromium/Carbonate Anionic DoubleHydroxide Clay

Example 1 was repeated except that a solution of Zn(NO₃)₂. 6H₂ O (29.8g, 0.10 moles) and Cr(NO₃)₃. 9H₂ O (13.3 g, 0.033 moles) in 70 mldeionised water was added to a solution of Na₂ CO₃ (31.8 g, 0.30 moles)in 300 ml deionised water at room temperature. The XRD of the product isshown in Table XRD-4.

Elemental analysis: 2.85% C; 44.7% Zn; 10.7% Cr. This corresponds to anempirical formula of Zn₆ Cr₁.8 (OH)₁₅.6 (CO₃)₀.9. 4H₂ O.

EXAMPLE 5 Preparation of a Lithium/Aluminium/Carbonate Anionic DoubleHydroxide Clay

A total amount of 250 ml of a 0.4M AlCl₃. 6H₂ O solution was addeddropwise to 600 ml of a mixture of 1.5M LiOH.H₂ O and 0.08M Na₂ CO₃ withvigorous stirring. The addition took 40-45 minutes. The gel-typeprecipitate was then heated at 65° C.±2 in a thermal bath with gentlestirring for about 18 hours. On cooling the white slurry was filteredand washed using hot deionised water. This was later dried at 70° C. inair overnight. The X-ray powder diffraction profile, Table XRD-5, wasthat of an anionic double hydroxide clay.

Elemental analysis: 2.95% C; 3.05% Li; 22.4% Al.

EXAMPLE 6 Preparation of Magnesium/Chromium/Carbonate Anionic DoubleHydroxide Clay

A solution of [Cr(H₂ O)₆ ]Cl₃ (178 g, 0.67 moles) and [Mg(H₂ O)₆ ]Cl₂(407 g, 2.00 moles) in 1.4 dm³ of distilled water was added at a rate ofabout 12 cm³ /minute to a vigorously stirred solution of Na₂ CO₃ (200 g,1.89 moles) and NaOH (280 g, 7.00 moles) in 2 dm³ of distilled water.The resulting reaction mixture was then heated to 65° C. for 18 hours.Vigorous stirring was maintained throughout this period. The slurry wasthen allowed to cool to room temperature. During this time theprecipitate partially settles from its mother liquor. The supernatantwas decanted and the slurry was concentrated by centrifuging (2000 rpm,about 1120 G, 1 hour) and decanting. The concentrated slurry was thenloaded into dialysis tubing (Medicell Visking size 6-27/32"). The sealedtubes were then continuously washed in distilled water until theeffluent water was chloride free (tested by 0.1 mol dm⁻³ AgNO₃ solution)and the conductivity was below 20 μS cm⁻¹. The dialysis tubes were thenopened and the recovered slurry was slowly dried in a fan oven at 60° C.

EXAMPLE 7 Preparation of Zinc/Aluminium/Carbonate Anionic DoubleHydroxide Clay

This material was made using a similar procedure described for the Mg-Crsystem above. A solution of [Al(H₂ O)₆ ]Cl₃ (162 g, 0.67 moles) and[Zn(H₂ O)₆ ]Cl₂ (489 g, 2.00 moles) in 1.4 dm³ of distilled water wasadded to a solution of Na₂ CO₃ (200 g, 1.89 moles) and NaOH (280 g, 7.00moles) in 2 dm³ of distilled water. The same work-up procedure was usedas described for the Mg-Cr material.

EXAMPLE 8 Preparation of Zinc/Iron (III)/Carbonate Anionic DoubleHydroxide Clay

This material was made using a similar procedure described for the Mg-Crsystem above. A solution of [Fe(H₂ O)₆ ]Cl₃ (181 g, 0.67 moles) and[Zn(H₂ O)₆ Cl₂ (489 g, 2.00 moles) in 1.4 dm³ of distilled water wasadded to a solution of Na₂ CO₃ (200 g, 1.89 moles) and NaOH (280 g, 7.00moles) in 2 dm³ of distilled water. The same work-up procedure was usedas described for the Mg-Cr material.

EXAMPLE 9 Calcination

The products of Examples 1 to 8 were calcined, at 450° C. (Examples 1 to5) or 400° C. (Examples 6 to 8 for 18 hours in air. The properties ofthe resulting catalysts were as follows:

    ______________________________________                                        Catalyst                                                                              Starting Material                                                                           Surface area                                                                              Elemental                                   Ref:    Prepared As In:                                                                             (m.sup.2 /g)                                                                              analysis                                    ______________________________________                                        A       Example 1     180         16.87% Al;                                  (Mg/Al)                           27.3% Mg                                    B       Example 2     150                                                     (Mg/Fe)                                                                       C       Example 3     156                                                     (Ni/Al)                                                                       D       Example 4                                                             (Zn/Cr)                                                                       E       Example 5     129         4.55% Li;                                   (Li/Al)                           35.5% Al                                    F       Example 6                                                             (Mg/Cr)                                                                       G       Example 7                                                             (Zn/Al)                                                                       H       Example 8                                                             (Zn/Fe)                                                                       ______________________________________                                    

X-ray diffraction patterns of the calcined materials are given in TablesXRD-6 to XRD-10.

EXAMPLES 10 TO 18 Preparation of glycol ethers

Tests were carried out in a fixed bed continuous flow reactor. A 10 dm³feed pot contained the reactants which were pumped through the 316stainless steel reactor (1/2"OD) under applied nitrogen pressure andcontaining pelleted catalyst. Two 1/16" thermocouples went on sides ofthe reactor right through to the centre of the catalyst bed. The productwas collected in an ice-cooled vial and analysed immediately on a PerkinElmer gas chromatograph equipped with a temperature programmingfacility. The injection port was held at 150° C. with the hot wiredetector at 150° C. Helium carrier gas flowed at 25 ml/min. The columnused was 5 meters×1/8 inch O.D. stainless steel column packed with 10%carbowax 20M on 60-80 mesh chromosorb was temperature programmed at 60°C. for 6 minutes and then 12° C./min to 180° C.

EXAMPLE 10

Starting reactant mole ratio ethanol/propylene oxide 10/1. Catalyst: A;weight-6.5 g, volume-10 ml, temperature 122°±1° C., feed rate-21 ml/hr,pressure-15 bar.

The results are given in Table A(1). 2° refers to the secondary glycolether, 1-ethoxy-2-propanol, and 1° refers to the primary glycol ether,2-ethoxy-1-propanol. Only traces (less than 70 ppm) of products otherthan 2° and 1° were obtained in this Example and also in Examples 8 to15. Secondary product selectivity is defined as 2°/(2°+1°)(%).

                  TABLE A(1)                                                      ______________________________________                                        Results of Example 10                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             23           94                                                 2             29           94                                                 3             28           94                                                 5             28           93                                                 7             28           92                                                 ______________________________________                                    

EXAMPLE 11

Starting reactant mole ratio ethanol/styrene oxide 10/1. Catalyst: A;weight-3.44 g, temperature-175°±3° C., volume-10 ml, flow rate-15 ml/hr,pressure-15 bar. The results are given in Table A(2).

                  TABLE A(2)                                                      ______________________________________                                        Results of Example 11                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       styrene oxide                                                                              selectivity                                        ______________________________________                                        1             24           47                                                 3             37           36                                                 4             86           38                                                 5             91           46                                                 6             92           56                                                 7             92           56                                                 8             94           58                                                 9             93           54                                                 10            92           58                                                 ______________________________________                                    

EXAMPLE 12

Starting reactant mole ratio ethanol/propylene oxide 10/1. Catalyst: B;weight-9.17 g, volume-15 ml, temperature-121°±2° C., feed rate-30 ml/hr,pressure-15 bar. The results are given in Table B(1).

                  TABLE B(1)                                                      ______________________________________                                        Results of Example 12                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             72           92                                                 2             75           83                                                 4             66           81                                                 7             50           86                                                 10            50           78                                                 ______________________________________                                    

EXAMPLE 13

Starting reactant mole ratio ethanol/styrene oxide 10/1; Catalyst: B;weight-6.34 g, temperature-175°±2° C., volume-15 ml, flow rate-15 ml/hr,pressure-15 bar. The results are given in Table B(2).

                  TABLE B(2)                                                      ______________________________________                                        Results of Example 13                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       styrene oxide                                                                              selectivity                                        ______________________________________                                        1              6           49                                                 2             28           79                                                 3             71           57                                                 4             69           43                                                 5             69           51                                                 6             70           38                                                 7             68           52                                                 8             66           47                                                 10            59           28                                                 ______________________________________                                    

EXAMPLE 14

Starting reactant mole ratio ethanol/propylene oxide 10/1. Catalyst: C;weight-18.31 g, volume-30 ml, temperature-120°±0.5° C., feed rate-30ml/hr, pressure 15 bar. The results are given in Table C.

                  TABLE C                                                         ______________________________________                                        Results of Example 14                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             15           97                                                 3             17           93                                                 5             17           100                                                7             16           90                                                 9             16           97                                                 ______________________________________                                    

EXAMPLE 15

Starting reactant mole ratio ethanol/propylene oxide 10/1. Catalyst: D;weight-17.55 g, volume-19 ml, temperature-120°±0.5° C., feed rate-20ml/hr, pressure-15 bar. The results are given in Table D(1).

                  TABLE D(1)                                                      ______________________________________                                        Results of Example 15                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             26           100                                                3             30           98                                                 5             34           100                                                7             34           98                                                 9             33           97                                                 14            34           94                                                 ______________________________________                                    

EXAMPLE 16

Starting reactant mole ratio ethanol/propylene oxide 10/1. Catalyst D;weight-9.6 g, volume-10 ml/hr, temperature-140° C., pressure-15 bar. Theresults are given in Table D(2).

                  TABLE D(2)                                                      ______________________________________                                        Results of Example 16                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             13           95                                                 2             19           94                                                 4             71           96                                                 7             77           98                                                 73            72           94                                                 ______________________________________                                    

EXAMPLE 17

Starting reactant mole ratio ethanol/styrene oxide 10/1. Catalyst: D;weight-12.66 g, temperature-175°±2° C., volume-12 ml, flow rate-18.5ml/hr, pressure-15 bar. The results are given in Table D(3).

                  TABLE D(3)                                                      ______________________________________                                        Results of Example 17                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       styrene oxide                                                                              selectivity                                        ______________________________________                                        2             27           50                                                 3             74           53                                                 4             93           69                                                 5             93           78                                                 6             92           80                                                 7             93           83                                                 8             90           80                                                 ______________________________________                                    

EXAMPLE 18

Starting reactant molar ratio ethanol/propylene oxide 10/1. Catalyst: E;weight-8.21 g, volume-25 ml, temperature-130°±3° C., feed rate-27 ml/hr,pressure 15 bar. The results are given in Table E.

                  TABLE E                                                         ______________________________________                                        Results of Example 18                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        2             38           95                                                 3             43           97                                                 5             34           100                                                8             25           95                                                 9             25           96                                                 11            24           95                                                 ______________________________________                                    

EXAMPLES 19 TO 21 Preparation of Glycol Ethers

Tests were carried out on catalysts F, G, and H as follows. Prior touse, the materials were ground and sieved with the particle size range0.1-1.0 mm being collected.

A premixed feed containing ethanol/propylene oxide (10:1 molar) was heldin a reservoir under a blanket of dry nitrogen. The catalyst bedcomprised of 10 cm³ of 0.5-1.0 mm particles loaded into a three-zonedfixed-bed reactor (0.9 cm ID) with a thermowell (0.48 cm OD). Threethermocouples were used to monitor the bed temperature profile. The runstart-up procedure involved pressurising the reactor to 50 barg with theliquid feed, establishing the required flow rate (20 cm³ h⁻¹, LHSV(liquid hourly space velocity) 2) and the increasing the reactortemperature to the operating condition of 100° C. The reactor liquideffluent was collected, over set intervals, at 0° C. and atmosphericpressure. A representative reactor product effluent was obtained after 5hours. Mass balances were typically 98% +.

The collected liquid product was analysed by gas chromatography. Twocolumns were used in this analysis. A Poropak QS column (1 m, 80-100mesh, 2 mm ID, 200° C.) to obtain accurate conversion data and aCP-Sil-5 WCOT fused silica capillary column (50 m, 0.25 mm ID, 10 minuteat 80° C., 8° C./minute to 200° C.) to obtain accurate selectivity data.

The results, obtained after 24 hours are given in Table F.

                  TABLE F                                                         ______________________________________                                        Results of Examples 19 to 21                                                  Example         Weight of % Conversion of                                                                          2° Product                        No.    Catalyst Catalyst  propylene oxide                                                                          Selectivity                              ______________________________________                                        19     F        9.4       42         94                                       20     G        7.6        6         84                                       21     H        13.0      13         83                                       ______________________________________                                    

EXAMPLE 22 First Cycle Rehydration

10.0 g of the calcined material A prepared as in Example 9 was taken andadded to 100 ml previously boiled water and cooled with bubbling N₂ forabout an hour. The material was then left overnight. It was then washedwith hot distilled water and partially dried under N₂ before being driedat 125° C. This material gave the XRD pattern of a regenerated anionicdouble hydroxide (hereafter referred to as regenerated 1st cycle) andthe reflections are shown in Table XRD-11. The material was thencalcined at 450° C. for 18 hours to generate the catalyst. The XRDpattern, given in Table XRD-12, showed two phases: a relatively smallamount of spinel and the expected pattern of a collapsed anionic doublehydroxide clay, i.e. MgO structure.

EXAMPLE 23 Second Cycle Rehydration

Example 22 was repeated using as starting material the product ofExample 22. The XRD powder pattern of the rehydrated material is shownin Table XRD-13, and that of the rehydrated recalcined material in TableXRD-14.

EXAMPLE 24

Example 22 was repeated using as starting material the product ofExample 23.

EXAMPLE 25 Fourth Cycle Rehydration

Example 22 was repeated using as starting material the product ofExample 24. The resulting calcined material had the XRD pattern shown inTable XRD-15, and had ²⁷ Al nmr peaks at 67.6 and 11.0 ppm.

EXAMPLE 26 Fifth Cycle Rehydration

Example 22 was repeated using as starting material the product ofExample 25.

EXAMPLE 27 Sixth Cycle Rehydration

Example 22 was repeated using as starting material the product ofExample 26.

EXAMPLE 28

Example 22 was repeated but this time carbon dioxide was bubbled throughundecarbonated distilled water. The XRD pattern was that of aregenerated anionic double hydroxide clay. Carbonate was confirmed to bethe interlayer anion from fourier transform i.r and microanalysis ofcarbon.

EXAMPLES 29 TO 33

The general method of glycol ether preparation described in Example 10was carried out using as catalysts the rehydrated-recalcined products ofExamples 22, 23, 25, 27 and 28 and using ethanol/propylene oxide 10/1 asfeedstock. Details are given below. In each case, only traces (less than70 ppm) of products other than 2° and 1° glycol ethers were obtained.The results are summarised graphically in FIGS. 1 and 2. FIG. 1 alsoincludes the results of Example 10, i.e. using a catalyst which has notbeen rehydrated and calcined. It can be seen thatrehydration-recalcination produces extremely beneficial effects.

EXAMPLE 29

The calcined material of Example 22 was tested: weight-6.7 g, volume-9ml, temperature-120° C., feed rate-10.5 ml/hr, pressure-15 bar. Theresults are given in Table 1.

                  TABLE 1                                                         ______________________________________                                        Results of Example 29                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             30           83                                                 2             37           95                                                 3             58           86                                                 4             59           89                                                 5             68           88                                                 6             67           93                                                 7             66           90                                                 8             74           88                                                 ______________________________________                                    

EXAMPLE 30

The calcined material obtained in Example 23 was tested. Weight-4.4 g,volume-6 ml, temperature-120° C., feed rate-7.2 ml/hr, pressure-15 bar.The results are given in Table 2.

                  TABLE 2                                                         ______________________________________                                        Results of Example 30                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             25           100                                                4             74           84                                                 6             76           84                                                 8             76           88                                                 10            75           81                                                 13            80           84                                                 ______________________________________                                    

EXAMPLE 31

The calcined material obtained in Example 25 was tested. Weight-5.4 g,volume-5 ml, temperature-120° C., feed rate-7.5 ml/hr, pressure-15 bar.The results are given in Table 3.

                  TABLE 3                                                         ______________________________________                                        Results of Example 31                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             11           100                                                4             61           85                                                 6             59           85                                                 8             65           83                                                 10            63           89                                                 ______________________________________                                    

EXAMPLE 32

The calcined material obtained in Example 27 was tested. Weight-7.3 g,volume-10 ml, temperature-120° C., feed rate-15 ml, pressure-15 bar. Theresults are given in Table 4.

                  TABLE 4                                                         ______________________________________                                        Results of Example 32                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        1             15           87                                                 2             14           87                                                 3             16           86                                                 4             23           88                                                 5             46           89                                                 6             45           88                                                 7             52           87                                                 9             53           86                                                 ______________________________________                                    

EXAMPLE 33

The calcined material obtained in Example 28 was tested. Weight-6.2 g,volume-9 ml, temperature-120° C., feed rate-10.5 ml/hr, pressure-15 bar.The results are given in Table 5.

                  TABLE 5                                                         ______________________________________                                        Results of Example 33                                                         Time on stream                                                                              % conversion of                                                                            2° Product                                  (hours)       propylene oxide                                                                            selectivity                                        ______________________________________                                        2             15           89                                                 5             42           82                                                 8             57           86                                                 ______________________________________                                    

EXAMPLE 34 (COMPARATIVE)

This Example uses a conventional cationic clay catalyst in thepreparation of a glycol ether. The catalyst was a fully hydrogen-ionexchanged clay, with no residual mineral acid, as described inEP-A-31687. The general method of Examples 10 to 18 was used, with thefollowing conditions:

Starting reactant mole ratio ethanol/propylene oxide 10/1. Catalyst H⁺ -montmorillonite, weight - 7.4 g, volume - 10 ml, particle size - 0.5-1.0mm, pressure - 15 barg.

The results are given in Table 6, and clearly show that, while the priorart catalyst is very active in the reaction, it is very much lessselective than the catalysts used in the present invention. Thecomparative tests were carried out at two different flow rates(LHSV=liquid hourly space velocity) and temperatures to illustrate thispoint.

                  TABLE 6                                                         ______________________________________                                        Results of Comparative Example 34                                             Time on stream                                                                          LHSV            % conversion of                                                                          2° Product                        (hours)   (h.sup.-1)                                                                            T/°C.                                                                          propylene oxide                                                                          selectivity                              ______________________________________                                         2        1        80     97         41                                       23        1       120     98         35                                       29        2       120     99          37*                                     ______________________________________                                         *The residual oxygenate products other than 1ethoxypropan-2-ol and            2ethoxypropan-1-ol, total around 1700 ppm, measured by gas chromatography     and mass spectrometry.                                                   

In the following tables of X-ray diffraction data, VS=very strong,S=strong, FS=fairly strong, M=medium, W=weak, VW=very weak and B=broad.

                  TABLE XRD-1                                                     ______________________________________                                        Powder X-ray diffraction data for uncalcined sample                           from Example 1                                                                d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        7.8       VS                                                                  3.9       S                                                                   2.6       S                                                                   2.3       W                                                                   1.9       W                                                                    1.53     S                                                                    1.50     FS                                                                  ______________________________________                                    

                  TABLE XRD-2                                                     ______________________________________                                        Powder X-ray diffraction data for uncalcined sample                           from Example 2                                                                d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        8.2       VS                                                                  4.0       S                                                                   2.7       S                                                                   2.4       W                                                                   2.0       W                                                                    1.57     S                                                                    1.54     M                                                                   ______________________________________                                    

                  TABLE XRD-3                                                     ______________________________________                                        Powder X-ray diffraction data for uncalcined sample                           from Example 3                                                                d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        7.9       VS                                                                  3.9       S                                                                   2.6       S                                                                   2.3       W                                                                   1.9       W                                                                    1.53     S                                                                    1.50     FS                                                                  ______________________________________                                    

                  TABLE XRD-4                                                     ______________________________________                                        Powder X-ray diffraction data for uncalcined sample                           from Example 4                                                                d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        7.7       S                                                                   3.8       M                                                                   2.7       BS                                                                  2.3       W                                                                    1.56     BM                                                                  ______________________________________                                    

                  TABLE XRD-5                                                     ______________________________________                                        Powder X-ray diffraction data for uncalcined sample                           from Example 5                                                                d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        7.8       VS                                                                  4.5       FS                                                                  3.8       S                                                                   2.6       S                                                                   2.3       BM                                                                  2.0       BM                                                                   1.48     M                                                                    1.45     M                                                                   ______________________________________                                    

                  TABLE XRD-6                                                     ______________________________________                                        Powder X-ray diffraction data for calcined Mg--Al sample                      from Example 6 reference A                                                    d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        2.6       BW                                                                  2.1       S                                                                   1.5       FS                                                                  1.2       W                                                                   ______________________________________                                    

                  TABLE XRD-7                                                     ______________________________________                                        Powder X-ray diffraction data for calcined Mg--Fe sample                      from Example 6 reference B                                                    d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        2.13      BS                                                                  1.50      BS                                                                  ______________________________________                                    

                  TABLE XRD-8                                                     ______________________________________                                        Powder X-ray diffraction data for calcined Ni--Al sample                      from Example 6 reference C                                                    d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        2.4       BS                                                                  2.1       S                                                                   1.5       S                                                                   1.3       W                                                                   1.2       W                                                                   ______________________________________                                    

                  TABLE XRD-9                                                     ______________________________________                                        Powder X-ray diffraction data for calcined Zn--Cr sample                      from Example 6 reference D                                                    d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        3.0       W                                                                   2.8       S                                                                   2.6       S                                                                   2.5       VS                                                                  2.1       W                                                                   1.9       W                                                                   1.6       M                                                                   1.5       M                                                                    1.38     M                                                                    1.36     W                                                                   ______________________________________                                    

                  TABLE XRD-10                                                    ______________________________________                                        Powder X-ray diffraction data for calcined Li--Al sample                      from Example 6 reference E                                                    d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        2.5       BW                                                                  2.0       BW                                                                  1.5       BW                                                                  1.4       BW                                                                  ______________________________________                                    

                  TABLE XRD-11                                                    ______________________________________                                        Powder X-ray diffraction data for rehydrated sample                           from Example 16                                                               d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                        7.8       VS                                                                  3.9       S                                                                   2.6       S                                                                   2.3       W                                                                   1.9       W                                                                    1.53     S                                                                    1.50     FS                                                                  ______________________________________                                    

                  TABLE XRD-12                                                    ______________________________________                                        Powder X-ray diffraction data for calcined sample from                        product in Example 16. Starred (*) values due to spinel                       (MgAl.sub.2 O.sub.4) and the unstarred due to anionic                         double hydroxide clay.                                                        d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                         2.4*     W                                                                   2.1       S                                                                    2.0*     FS                                                                   1.6*     W                                                                   1.5       FS                                                                   1.4*     FS                                                                  ______________________________________                                    

                  TABLE XRD-13                                                    ______________________________________                                        Powder X-ray diffraction data for rehydrated sample from                      Example 17. Starred (*) values due to spinel (MgAl.sub.2 O.sub.4)             and the unstarred due to anionic double hydroxide clay.                       d/Å    Relative Intensity (I/I.sub.o)                                     ______________________________________                                        7.8        VS                                                                 3.9        S                                                                  2.6        S                                                                   2.4*      W                                                                  2.3        FS                                                                  2.02*     W                                                                   1.98      W                                                                   1.53      FS                                                                  1.50      S                                                                   1.4*      FS                                                                 ______________________________________                                    

                  TABLE XRD-14                                                    ______________________________________                                        Powder X-ray diffraction data for calcined sample from                        Example 17. Starred (*) values due to spinel (MgAl.sub.2 O.sub.4)             and the unstarred due to anionic double hydroxide clay.                       d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                         4.7*     W                                                                    2.8*     W                                                                    2.4*     FS                                                                  2.1       S                                                                    2.0*     S                                                                    1.6*     S                                                                   1.5       S                                                                   ______________________________________                                    

                  TABLE XRD-15                                                    ______________________________________                                        Powder X-ray diffraction data for calcined product in                         Example 21. Starred (*) values due to spinel and the                          unstarred due to anionic double hydroxide clay.                               d/Å   Relative Intensity (I/I.sub.o)                                      ______________________________________                                         4.7*     W                                                                    2.9*     W                                                                    2.4*     S                                                                   2.1       S                                                                    2.0*     S                                                                    1.6*     VW                                                                  1.5       W                                                                    1.4*     S                                                                   ______________________________________                                    

We claim:
 1. A process for the preparation of a glycol ether by reactingan olefin oxide with an excess of an alcohol over a catalyst;characterized in that the catalyst comprises a material which has beenprepared by calcination of an anionic double hydroxide clay having astructure comprising magnesium and aluminum in combination, following byrehydration and subsequent recalcination.
 2. A process as claimed inclaim 1, in which the olefin oxide has up to 10 carbon atoms.
 3. Aprocess as claimed in claim 1, in which the alcohol has up to 8 carbonatoms.
 4. A process as claimed in claim 1, in which ethanol is reactedwith propylene oxide.
 5. A process as claimed in claim 1, carried out ata temperature of from 0° to 200° C.
 6. A process as claimed in claim 1,in which the calcination of the anionic double hydroxide clay comprisedheating to a temperature of from 300° to 550° C. under non-reducingconditions.
 7. A process as claimed in claim 6, in which the calcinationof the anionic double hydroxide clay comprised heating in air.
 8. Aprocess as claimed in claim 8, in which the rehydration has been carriedout using water substantially free from dissolved ions.
 9. A process asclaimed in claim 2 in which the alcohol has up to 8 carbon atoms.